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Appendix E - Broadband Technology Primer

What is Broadband?

There is no universally accepted definition of what constitutes broadband connectivity. It is however; important to recognize that in order to take advantage of the Internet's potential, connecting at a reliable, high transfer rate will be key. Advanced applications like distance education, tele-health, and e-business require broadband access. Depending on the source, definitions of broadband vary between 200kpbs and 30Mbps with most centering around the T1 level of 1.544 bi-directional Mbps. The National Broadband Taskforce, defined broadband as "a minimum two-way, or symmetrical, transmission speed of 1.5Mbps per individual user" with the overall goal of providing "a high-capacity, 2-way link between an end user and access network suppliers capable of supporting full-motion, interactive video applications."

When deciding on what constitutes broadband one must also take into account the services that are currently available in the geographic area of concern. In the eyes of many communities broadband may simply be defined as "anything faster than our dial-up modem".

Technologies

The use of broadband technologies across North America is growing rapidly. A survey conducted by Kinetic Strategies found there are 9.4 million residential customers of broadband Internet services in North America, which includes 8.2 percent household penetration. In addition, the study found that cable is outpacing digital subscriber line service, with 70 percent market share. Cable modem providers continue to dominate DSL providers, with an estimated 6.4 million cable modem customers in the United States and Canada, equal to 70 percent of the market. In comparison, DSL providers served 2.9 million residential subscribers, according to the survey.

xDSL

A Digital Subscriber Line (DSL) is a very high-speed connection that uses the same wires as a regular telephone line. ADSL is a distance-sensitive technology: As the connection's length increases, the signal quality decreases and so does the connection speed. The limit for ADSL service is 5,460 meters, although for speed and quality of service reasons many ADSL providers place a lower limit on the distances for the service. At the extremes of the distance limits, ADSL customers may see speeds far below the promised maximums, while customers nearer the central office have faster connections and may see extremely high speeds in the future. ADSL technology can provide maximum downstream (Internet to customer) speeds of up to 8 megabits per second (Mbps) at a distance of 1,820 meters, and upstream speeds of up to 640 kilobits per second (Kbps). In practice, the best speeds widely offered today are 1.5 Mbps downstream, with upstream speeds varying between 64 and 640 Kbps.

ADSL uses two pieces of equipment, one on the customer end and one at the Internet service provider. At the customer's location there is a DSL transceiver, and the DSL service provider has a DSL Access Multiplexer (DSLAM). Most residential customers call their DSL transceiver a "DSL modem. It is simply a piece of equipment that connects the customers equipment to the to the DSL line. The DSLAM at the access provider is the equipment that really allows DSL to happen. A DSLAM takes connections from many customers and aggregates them onto a single, high-capacity connection to the Internet. The DSLAM provides one of the main differences between user service through ADSL and through cable modems. Because cable-modem users generally share a network loop that runs through a neighborhood, adding users means lowering performance in many instances. ADSL provides a dedicated connection from each user back to the DSLAM, meaning that users won't see a performance decrease as new users are added.

Types of DSL

Asymmetric DSL (ADSL) - Most homes and small business users are connected to an ADSL line. ADSL divides up the available frequencies in a line on the assumption that most Internet users look at, or download, much more information than they send, or upload. Under this assumption, the connection speed from the Internet to the user is 3-4 times faster than the connection from the user back to the Internet.

Very high bit-rate DSL (VDSL) - This is a fast connection, but works only over a short distance.

Symmetric DSL (SDSL) -This connection, used mainly by small businesses, doesn't allow you to use the phone at the same time, but the speed of receiving and sending data is the same.

Rate-adaptive DSL (RADSL) - This is a variation of ADSL, but the modem can adjust the speed of the connection depending on the length and quality of the line. Current technology can provide a theoretical maximum of up to 7 megabits per second, and research promises even greater performance in the future with protocols VDSL.

Cable Modems

When a cable company offers Internet access over the cable information is sent from the Internet to an individual computer - into a 6 MHz channel. On the cable, the data looks just like a TV channel. Internet downstream data takes up the same amount of cable space as any single channel of programming. Upstream data -- information sent from an individual back to the Internet -- requires even less of the cable's bandwidth, just 2 MHz.

Putting both upstream and downstream data on the cable television system requires two types of equipment: a cable modem on the customer end and a Cable-Modem Termination System (CMTS) at the cable provider's end. A CMTS will enable as many as 1,000 users to connect to the Internet through a single 6 MHz channel. Since a single channel is capable of 30-40 megabits per second of total throughput, this means that users may see far better performance than is available with standard dial-up modems. The single channel aspect, though, can also lead to one of the issues some users experience with cable modems. If you are one of the first users to connect to the Internet through a particular cable channel, then you may have nearly the entire bandwidth of the channel available for your use. As new users, especially heavy-access users, are connected to the channel, you will have to share that bandwidth, and may see your performance degrade as a result. It is possible that, in times of heavy usage with many connected users, performance will be far below the theoretical maximums. The good news is that the cable company adding a new channel, and splitting the base of users can resolve this particular performance issue. Another benefit of the cable modem for Internet access is that, unlike ADSL, its performance doesn't depend on distance from the central cable office. A digital DATV system is designed to provide digital signals at a particular quality to customer households.